The sequence of appearance of HCV-RNA and of the different antibodies to hepatitis C virus (HCV) epitopes following experimental infection of two chimpanzees with HCV, have been investigated. The chimps were infused with unprocessed, pooled plasma from donations that were non-reactive for anti-HCV. Serum samples were obtained prior to infusion, and then weekly subsequent to infusion. These samples were tested for anti-HCV, HBsAg, anti-HBs, anti-HBc and alanine aminotransferase (ALT). Serum samples were also tested for the presence of HCV-RNA by polymerase chain reaction assay (PCR) and for antibodies to c100-3, C22-3, c33c and 5-1-1 by the immunoblot, RIBA II test. The two chimpanzees showed different patterns in the sequential and temporal appearance of HCV-RNA and of antibodies to the different HCV epitopes. HCV-specific genomic sequences were detected in serum within one week after infusion in one animal and 9 weeks in the other chimp. Elevations in ALT values were observed 3 weeks subsequent to infusion in both animals.